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MS2 Renal > 9/8- Review of Renal Physiology > Flashcards

9/8- Review of Renal Physiology Flashcards

1
Q

T/F: there are a few, scattered glomeruli in the renal medulla?

A

False; the renal medulla = tubules + vessels (no glomeruli)

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2
Q

Describe the vasculature of the kidney?

A

Renal artery -> afferent arteriole -> glomerula caps -> efferent arteriole -> peritubular caps

Vasa recta = peritubular caps of the juxtamedullary nephrons

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3
Q

What comprises the glomerular filtration barrier?

A
  1. Capillary endothelial cells
  2. Glomerular basement membrane
  3. Glomerular epithelial cells (podocytes)
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4
Q

What are barriers to glomerular filtration?

A
  • Size (MW under 5,500 = freely filtered)
  • Charge (major determinant for MW 5.5-44K, fixed negative charges on filtration surface)
  • Shape (minor determinant)
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5
Q

Names for inner tubule surface?

A

Luminal or apical

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6
Q

Names for outer tubule surface?

A

Peritubular or basolateral

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7
Q

What is reabsoprtion?

A

Transport of water/solutes form inside -> outside the tubule

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8
Q

What is secretion?

A

Transport of water/solutes form outside -> inside tubule

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9
Q

Urine volume = ?

A

Urine volume = filtration - reabsorption + secretion

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10
Q

What is the role of the proximal nephron (PCT or PST)?

A

Bulk reabsorption of water and solutes (Na, Cl, HCO3, glucose)

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11
Q

What is the role of the Loop of Henle (tDLH, tALH, TALH)?

A
  • Moderate solute reabsorption
  • Urine concentration and dilution
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12
Q

What is the role of the distal nephron (DCT, CND, collecting tubule- initial, cortical, outer/inner medullary)?

A
  • “Fine-tune” urine composition
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13
Q

What is the distribution breakdown of water in the extracellular vs. intracellular compartment?

A

Extracellular ~40% (17 L)

  • Blood plasma = 3 L
  • Interstitial fluid = 13 L
  • Transcellular fluid = 1 L

Intracellular ~ 60% (25 L)

(Total body water = 42 L)

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14
Q

Solute composition of plasma?

A
  • Na: 142
  • K: 4.4
  • Ca: 1.2 (ionized)
  • Mg: 0.6 (ionized)
  • Cl: 102
  • HCO3-: 22
  • Proteins: 7 g/dL
  • Glucose: 5.5 mM

pH = 7.4

Osmolality = 291

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15
Q

Volume balance: synonymous terms for intravascular volume?

A
  • Plasma volume
  • Effective circulating volume
  • 1/4 of extracellular fluid (ECF) volume

These determine blood pressure

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16
Q

In what conditions will you see a dissociation between total body volume and effective circulating volume?

A

Some disease states:

  • CHF
  • Cirrhosis
  • Kidney disease
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17
Q

T/F: Volume balance = water balance?

A

FALSE

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18
Q

Change in water balance changes what factors? Salt balance?

A

Change in water balance:

  • Relatively BIG change in osmolarity
  • Relatively SMALL change in ECF volume

Change in salt balance:

  • Reflected by ECF volume
  • Represents a minimal change in serum sodium (Na) osmolarity
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19
Q

Describe the renin-angiotensin-aldosterone axis (picture)

A
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20
Q

What triggers renin release? Inhibits?

A

Stimulated by:

  • Hypotension
  • Increased sympathetic outflow to JGA
  • Renal hypoperfusion (renal baroreceptors)
  • Endothelin, PGE2, PGI2

Inhibited by:

  • Hormones (Angiotensin II, AVP)
  • Other: high [K], nitric oxide
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21
Q

What triggers anigotensin II release?

A
  • Increase systemic blood pressure
  • Aldosterone release
  • Increase sensitivity of Tubuloglomerular feedback
  • Stimulate Na-H countertransport
  • Stimulate AVP and thirst centers
  • Efferent arteriolar vasoconstriction
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22
Q

ICF volume is a reflection of what?

A

Water balance/osmolarity

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23
Q

What are sensors of ICF volume?

A

Osmoreceptor input

24
Q

What are effector pathways of ICF volume

A
  • AVP (via ADH)
  • Thirst
25
Q

What solutes are excreted by tubules:

  • Completely
  • Partially
  • Not at all
A
  • Completely: PAH
  • Partially: creatinine, Na
  • Not at all: glucose, bicarbonate
26
Q

Equation for arterial content?

A

(RPFa)(Px,a)

27
Q

Equation for venous content?

A

(RPFv)(Px,v)

28
Q

Equation for urine content?

A

(V)(Ux)

29
Q

Equilibrium equation?

A

(RPFa)(Px,a) = (RPFv)(Px,v) + (V)(Ux)

Basically, arterial content = venous content + urine content

30
Q

Equation if solute is completely extracted?

A

Px,v = 0,

therefore: (RPFa)(Px,a) = (V)(Ux)

and

(RPFa) = (Ux)(V)/(Px,a)

31
Q

What is clearance?

A

Cx = (Ux)(V)/(Px)

32
Q

What are characteristics of the ideal marker to estimate glomerular filtration rate? What is it?

A
  • Freely filtered in the glomerulus
  • No tubular reabsorption or secretion
  • Not synthesized or metabolized
  • Physiologically inert

This is Creatinine

  • Endogenous product of muscle metabolism
  • Easy to measure its value in the blood
  • Stable rate of production
33
Q

Is creatinine filtered? Reabsorbed? Excreted?

A
  • Filtered
  • NOT reabsorbed
  • Secreted
34
Q

What is the rate of creatinine production for males/females?

A

Males: 15-20 mg/kg ideal body weight

Females: 15-20 mg/kg ideal bod weight

35
Q

Alternate markers to creatinine?

A
  • Inulin (gold standard)
  • B12
  • Iothalamate
  • EDTA
36
Q

Clearance of creatinine estimates what?

A

The glomerular filtration rate (GFR)

37
Q

What is normal GFR?

A

100-125 mL/min (adults)

  • Males > females
  • Declines with age
38
Q

Does stable serum creatinine = stable kidney disease?

A

No

  • The sCr is not a great marker also because it is maintained despite loss of GFR due to tubuloglomerulofeedback (recruitment of other gloms) and increased tubular Cr secretion 15% to 35%.
39
Q

Results of regulation of GFR (glomerulotubular balance)?

A

Glomerulotubular balance:

  • No change in fractional excretion/reabsorption
  • High GFR -> high absolute reabsorption / excretion
  • Low GFR -> low absolute reabsorption / excretion
  • Prevents excessive changes in solute excretion
40
Q

How is GFR regulate?

A

1. Tubuloglomerular feedback (TGF)

  • Macula densa (MD) senses changes in solute delivery (MD = specialized cells near distal tubule & vascular pole)
  • Results in release of vasoactive substances -> change GFR

2. Neurohormonal effects- Vasoconstriction

  • Angiotensin II: Arteriolar vasoconstricton efferent > afferent
  • Arginine vasopressin: Renal vasoconstriction medulla > cortex
  • Sympathetic nervous system activation
  • Modulators: epinephrine, endothelins, leukotrienes
41
Q

Does anigotensin II vasoconstrict the afferent or efferent arterioles more?

A

Efferent > afferent

42
Q

What is the range of urine osmolality?

A

30-1200 mOsm (daily solute exretion ~ 600 mOsm)

43
Q

What is the lowest possible urine volume? Highest?

A

Lowest: V = 600/1200 0.5 L/day

Highest: V = 600/30 = 20 L/day

44
Q

What is the osmolarity of the fluid entering the descending thin limb? In the medullary interstitium?

A
  • Fluid entering tDL: 300 mOsm
  • Medullary interstitium: 1200 mOsm

Established by the countercurrent multiplier system

45
Q

What is arginine vasopressin?

A

Aka aldosterone or anti-diuretic hormone (ADH)

46
Q

What is the mechanism of action of ADH? What stimulates/suppresses it?

A
  • Insertion of water channels (aquaporins) into apical membrane in collecting ducts
  • Upregulate Na/K/Cl cotransport in thick limb
  • Insertion of urea transporters (UT1) into apical membrane in medullary collecting ducts
  • Stimulated by hyperosmolarity
  • Suppressed by hypoosmolarity
47
Q

What are major hormones controlling phosphorus regulation?

A

Parathyroid hormone (PTH)

  • Decreases PO4 reabsorption (increases excretion)
  • Downregulates apical transporter expression 1,25-dihydroxy vitamin D
  • Increases PO4 reabsorption (decreases excretion) at distal nephron

Increase PO4 excretion:

  • Increase intake
  • ANP
  • Glucocorticoids
  • Acidosis
48
Q

Describe calcium regulation in terms of Na and other hormones?

A
  • Increased Na reabsoprtion -> increased Ca reabsorption (and vice versa); it follows Na!

- PTH: increases Ca reabsorption in TAL, DCT, CCT

  • Vitamin D: increases Ca reabsorption in distal nephron

- Loop diuretics: decrease Ca reabsorption

49
Q

What is normal blood pH? Minimal urine pH?

A
  • Normal blood: 7.4
  • Minimal urine: 4.4
50
Q

What is acidemia? What causes it?

A

Low pH of blood, caused by either:

  • Respiratory acidosis (high PCO2)
  • Metabolic acidosis (low HCO3)

Acidemia does NOT = acidosis (acidemia is the net pH change; acidosis is the process leading to this)

51
Q

What is alkalemia? What causes it?

A

High pH of blood caused by either:

  • Respiratory alkalosis (low PCO2)
  • Metabolic alkalosis (high HCO3)

Alkalemia does NOT = alkalosis

52
Q

What are the ECF buffers? Relative importance/effectiveness?

A
  1. Bicarbonate (CO2/HCO3)
  2. Proteins
  3. Phosphate (H2PO4/HPO4)
53
Q

What are the relevant equations for CO2/HCO3 buffer pair?

A

pKa of the bicarbonate buffer system = 6.1

pH = 6.1 + log (HCO3)/(CO2)

pH = 6.1 + log (HCO3)/(PCO2 x 0.03)

54
Q

Why is bicarbonate buffer system (pKa = 6.1) better than phosphate (pKa = 6.8)?

A
  • [HCO3] >> [total phosphates]
  • Open system (respiratory adjustment of CO2 and renal adjustment of HCO3)
55
Q

How does the kidney respond to respiratory processes? (speed, HCO3 handling…)

A
  • Slow (hours or days)
  • Reclamation of filtered HCO3
  • Increased titratable acid excretion
  • Very increased ammoniagenesis
  • H secretion = HCO3 reabsorption
56
Q

How does the kidney respond to metabolic alkalosis?

A

Suppression of proximal H+ secretion

  • Inhibit basolateral Cl-HCO3 exchange
  • Increase HCO3 paracellular backleak

Suppression of ammoniagenesis

Inhibit H+ secretion in Cortical Collecting Duct

  • Decrease alpha-type intercalated cells (H+ secretion)
  • Increase beta type intercalated cells (HCO3 secretion)
57
Q

Correction of metabolic alkalosis is very sensitive to ________. Elaborate

A

Correction of metabolic alkalosis is very sensitive to ECF volume status

  • Volume depletion limits ability to correct alkalosis
    1. Decreased GFR = decreased filtered load HCO3
    2. Decreased Na delivery = decreased Na reabsorption (Na-H exchange)
    3. Decreased ECF volume = Increased aldosterone (Increased H+ secretion)

MS2 Renal (25 decks)

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